There is known an apparatus in which a sliding member 30 movable in a closing/opening direction (vertical direction) relative to a molding target inside a molding chamber has a backplate member 31 and a swivel member 32, a single convex portion 33 is provided substantially in the center of the lower face of the backplate member 31, and springs 34 are arranged around the convex portion 33 (refer to JP 2007-320102A). In this apparatus, the swivel member 32 may be inclined in any direction within a certain angle range with respect to a horizontal plane by using the convex portion 33 as a center. For this reason, even when an upper face of the molding target is not horizontal but inclined, the swivel member (32) is inclined along the upper face of the molding target so as to make contact with the molding target without a gap.